1. Field
Aspects described relate generally to electrical interconnection systems and more specifically to improved signal integrity in interconnection systems.
2. Discussion of Related Art
In various electrical interconnection systems, separable multi-pin connectors are commonly used. Single-ended and differential pair electrical paths that carry signals in the 1 to 20 Gigabit per second range are provided by signal carrying structures such as cables or integrated circuit packages. Such electrical paths are often present between circuit boards, such as a daughter card and a backplane. Accordingly, separable connectors that carry signals at frequencies in this range are known. Though, it can frequently be a challenge in designing an electrical connector to provide a suitable number of signal paths in a relatively confined area in which all of the signal paths have electrical properties that support a desired level of performance for an overall electronic system.
In situations where a connector does not have pre-designated signal or ground conductors, the connector may be referred to as an “open pin field connector.” For open pin field connectors, electrical characteristics of the connectors, such as insertion loss, signal reflections due to impedance mismatch, crosstalk between different signal conductors, or the like, may be controlled by appropriately choosing how connector pins are assigned. For example, some connector pins may be assigned to carry signals or may be paired to carry differential signals. Some connector pins may be assigned to serve as high frequency digital ground connections. These grounds may be connected to earth ground or may carry a fixed voltage power supply or power return. In some cases, digital ground connections are used simultaneously with power return connections. Also, some signals are assigned to carry relatively low speed signals.
In an open pin field connector, pin assignments may be made to separate high speed signal conductors or to surround high speed signal conductors with grounds. For example, if a connector includes conductive pins that are arranged in a two dimensional rectangular array of rows and columns, it is possible to assign pairs of horizontally adjacent conductors to serve as the plus and minus signal pins for a differential signal in an alternating pattern with pairs of horizontally adjacent ground return pins. The pattern of signal pins may be staggered by two positions from row to row. Such an arrangement provides a differential pair and ground pair checkerboard pattern. Similar configurations may arise for vertically paired signal conductors and paired grounds.
An alternative approach to achieving desired electrical properties for signal paths through an electrical connector is to designate certain conductors within the connector to carry signals and others to be connected to ground. When it is known a priori which conductors are to carry signals and which are to be connected to ground, the shape and position of the conductors can be tailored to their function. For example, signal conductors designated to be a pair to carry a differential signal may be routed close to each other. Conductors designated to be connected to ground may be made wider than those carrying high speed signals and may be positioned to shield high speed signals.
Also, when the intended functions of conductors in a connector are pre-assigned, lossy material may be incorporated into the connector to increase performance of the connector. The lossy material, for example, may contact the ground conductors as a way to reduce resonances in the connector.
Though connectors with conductors having pre-assigned functions may provide better performance, historically, many connectors have been open pin field connectors. Open pin field connectors provide greater flexibility to designers of electronic systems. Moreover, once a system has been designed with a connector, it is desirable if upgrades to that system use the same connector or compatible connector to allow older and newer components to be interconnected. For these and other reasons, open pin field connectors are still widely used.